Crabs: To have or have not

[pirate]

I have 10-15 blue leg hermits, and a tiger pistol shrimp, so I'm not really sure how many are left. Its fun to watch them wander around, and I guess they help to clean my tank can't really tell. I keep buying them so I guess I like them.
they seem to leave everthing alone in my tank as far as I can tell, but I also don't have a lot of too expensive corals so if they eat one or two well thats nature.